Electron discharge tube and the like



March 30, 1937.

E. J. HOFFMAN I ELECTRON DISCHARGE TUBE AND THE LIKE Filed Aug 14, 1936INVENTOR ATTORNEY Patented Mar. 30,1937

UNITED STATES PATENT OFFICE Eugene J. Hoffman, St. Marys, Pa., assignorto Hygrade Sylvania Corporation, Salem, Mass., a. corporation ofMassachusetts Application August 14, 1936, Serial No. 95,981

Claims.

This invention relates to electron discharge tubes and more particularlyto such devices as thermionic valves employing a filamentary cathode.

5 An object of the invention is to provide an improved manner ofsupporting and anchoring a filament in a thermionic tube.

One of the chief causes of so-called microphonic noises during theoperation of a filament type tube or valve, is the loose connection thatusually exists between the bight of the filament and its resilientsupporting hook. I have found that by employing special materials tobond. the

filament bight rigidly to its supporting hook, these microphonic noisesare materially reduced. Preferably the bonding material is such that itmay be applied in liquid or semi-liquid form after the assembly of themount so that the subsequent heat treatment of the assembled tube willcause a hardening of the bonding material.

Accordingly a feature of the present invention relates to a thermionicvalve or the like, having a filament with a bight which is supported bya resilient hook, the bight being integrally and rigidly bonded to thehook by specially chosen materials which will not interfere with theproper operation of the valve as for example releasing undesirablegases, causing chemical corrosion between the bight and the hook, andthe like.

A further feature relates to the novel organization, arrangement andrelative location of parts which go to make up a thermionic valve mountof the filamentary cathode type which is singularly free frommicrophonic noises during operation.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims.

While the invention will be described as embodied in one particular typeof thermionic valve or tube it will be understood that this is donemerely for purposes of explanation and not by way of limitation.Accordingly in the-drawing,

Fig. l is a view, partly sectional, of a triode mount embodying featuresof the invention.

Fig. 2 is an enlarged View of the manner of bonding the filament bightto its supporting hook.

Referring to Fig. 1 there is shown a typical mount for a three elementtube or triode. The mount comprises a base or stem 1 into which aresealed the various lead-in and support wires 2 to 8 inclusive.The'support wires are preferably spaced apart at their upper ends by asuitable insulator disc such as a mica disc 9 which may be attached asfor example by the metal tabs or straps It! to the tubular plate oranode II, the latter being carried by the wires '2 and 8. Likewise thewire-wound grid 12 is carried by the wires 3 and 1. The cathode I3 is inthe form of a wire or ribbon filament provided with a coat-' ing of asuitable electron emissive material or materials as is well understoodin the art. The free ends of the filament l3 are welded or otherwiseconductively attached to the wires 4 and 6, while the bight of thefilament is supported by a fine spring wire hook M. For this purposethere is provided the wire arbor 5 which preferably extends upwardlyoutside the plate H and projects upwardly beyond the mica disc 9. Thefine spring wire hook I4 may be welded or otherwise fastened to theupper end of arbor 5 as shown more clearly in Fig. 2. The center of disc9 is provided with an opening IE to allow the hook I4 to extendtherethrough to engage the bight of the filament l3. In the usual tube,reliance is placed upon the natural springiness of the hook to maintainthe filament taut and to maintain the hook in contact with the bight. Ihave found however that this loose contact between the filament hook andthe bight of the filament is the cause of very much microphonicdisturbance when the tube is in operation. I have also found that thismicrophonism can be very materially reduced by rigidly bonding thefilament hook to the filament bight. However because of the limitationsof temperature, gas-release and the like the usual materials employedfor bonding are not suitable as applied to thermionic valves or tubes.Furthermore because of the delicate nature of the filament and its hook,and also because of the necessity of maintaining the spacing of theelectrodes undisturbed once they are properly assembled I have found itnecessary to employ as the bonding material a substance that can beapplied in the liquid or semi-liquid state but which upon suitabledrying or heat treatment hardens to form a solid rigid bond. As examplesof such materials I may mention a powdered refractory metal oxide ormixture of such oxides carried in a liquid vehicle or binder which canbe volatilized during the heat treatment of the tube without danger ofcontaminating or otherwise interfering with the desired characteristicsof the tube. For example beryllium oxide may be mixed with a suitablebinder preferably, although not necessarily, an inorganic binder such asa water or alcohol solution of a hydrolyzed nitrate, to form a liquid orsemi-liquid paste.

When the mount has been completely assembled and the parts adjusted totheir proper spaced. relation, and with the filament bight in engagementwith the hook, a small quantity of the above-described material isapplied as for example by means of a small brush to the hook as shown inFig. 2. The material is then allowed to dry either naturally or byheating it to drive off the liquid vehicle whereupon the refractoryoxide solidifies to form a rigid bond l6 between the filament bight andthe hook, thus preventing relative movement therebetween.

The following is one particular method of preparing the binder or liquidvehicle for the refractory metal oxide which has been found.satisfactory. Beryllium or aluminum preferably in powdered form is addedto an acid such for example as nitric acid, the metal and acid beingpresent preferably in respective molar proportions in excess of thosenecessary to produce a normal orneutral nitrate. The resultant solutionhas the apparent characteristics of a hydrolyzed nitrate of aluminum orof beryllium depending upon which metal is used. This nitrate is thendried in any suitable manner preferably over a water bath to produce aclear non-crystallized solid substance. This solid is then dissolved inwater or in an alcohol to produce the viscous liquid vehicle to whichthe powdered refractory metal oxide such as beryllium oxide, aluminumoxide may be added. This mixture is then applied to the filament hook asabove-described.

The above-described procedure produces a solid rigid insulating bondbetween the filament bight and its hook. In certain cases however it maybe desirable to have this solid bond conductive. In such cases thebonding material may be applied in the form of a solution of Aquadagdiluted with ammonia and water or alcohol.

While specific materials and methods of preparation have been describedherein various changes and modifications may be made therein withoutdeparting from the spirit and scope of the invention.

What I claim is:

1. In a radio tube mount the combination of, a filament having a bightportion, a filament tensioning member having a hook engaging said bight,and a solid mass of refractory material rigidly bonding said bight tosaid hook.

2. In a radio tube mount the combination of,

a filament having a bight portion, a filament tensioning member having ahook engaging said bight, and a solid mass of a refractory metal oxiderigidly bonding said bight to said hook.

3. In a radio tube mount the combination of, a filament having a bightportion, a filament tensioning member having a hook engaging said bight,and a quantity of a refractory material capable of being applied to thebight and hook in a semi-liquid condition and capable of being dried toform a solid rigid bond between the bight and hook.

4. In a radio tube mount the combination of, a filament having a bightportion, a filament tensioning member having a portion engaging saidbight; and a mass of refractory powdered material having a hydrolyzedmetallic salt binder to form a solid rigid bond between said bight andtensioning member.

5. In a radio tube mount the combination of, a filament having a bightportion, a filament tensioning member having a portion engaging saidbight, and a solid mass of refractory material forming a rigid bondbetween the bight and tensioning member and consisting of a driedsolution of Aquadag.

EUGENE J. HOFFMAN.

